As a thought experiment, suppose I modified the value of $c$ (speed of light) in some local region and attempted to measure it with a clock placed in that same region. I will denote this new unmeasured speed $c'$. If I tried to measure $c'$ with a clock then (based on my understanding of physics) I would still arrive at the conclusion that $c=c'$ since the rate at which physical processes evolve in a region is dependent on the value of light-speed in that region. Consequently the rate at which the internal processes of a clock evolve will be dependent on the value of light-speed as well. This will effectively change the way I measure $c'$ and cancel out any measurable $\Delta c$.


Based on my reasoning above, I feel it is necessary to ask...

1.) What do exactly do cosmologists mean when they assert that the inflationary period was a period where the speed of light was different than what we measure it to be today?

2.) How do cosmologists define a value of light-speed which is different from our current value?

3.) How could a cosmologist measure a value of the speed of light which is different from its current value?

4.) Were is my logic flawed?

Additional Note:

I understand they did this because it could explain the isotropic nature of the physical characteristics space-like separating events; that is, I understand why they did it just not how they model it theoretically.

  • $\begingroup$ I think you should cut this question down to your intro paragraph point. I'd phrase it something like "is our definition of time based on c such that if c changed we would still measure it to be the same?". As your current question stands, I think it's off topic for more than one reason. $\endgroup$ – Brandon Enright Jun 25 '14 at 19:01
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    $\begingroup$ During the inflationary period, the speed of light was exactly the same as nowadays, since that speed is a constant in General Relativity and inflationary models adopt GR. $\endgroup$ – Valter Moretti Jun 25 '14 at 20:12
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    $\begingroup$ please give a link or a reference for us to find a link for this assertion "cosmologists...speed of light different" . In my books the inflationary period was hypothesized because in the old Big Bang model one could not explain the isotropy in CMB because in the old BB the regions at the time of decoupling of the photons would not thermodynamically come into equilibrium because there were inaccessible regions due to the velocity of light being necessary for thermodynamics. The inflationary period introduced quantum mechanics and has an inflaton field which homogenizes everything then. $\endgroup$ – anna v Jul 2 '14 at 18:30

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